Ball-arranging substrate for forming bump, ball-arranging head, ball-arranging device, and ball-arranging method

ABSTRACT

A ball-arranging substrate comprising a substrate with a main surface, a plurality of ball-arranging holes formed on the main surface for sucking and holding minute electroconductive balls at the locations corresponding to those of electrodes formed on a semiconductor device or a printed circuit board, wherein when light illuminates the ball-arranging surface to allow optical recognition of the arrangement of the minute electroconductive balls by means of the light reflected by the minute electroconductive balls and by the main surface, the wave length of the light of the light source is set in the range of 300 to 900 nm, and the reflectivity is made not more than 50% based on the light source. A reflective mirror should be provided on the rear surface of the substrate opposite to the light source, in the case when the substrate is transparent to the irradiated light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate, a head, an apparatus and amethod each for arranging a plurality of minute electroconductive balls,which are bonded to form bumps on the electrodes of a semiconductorelement, printed circuit board (PCB), etc., wherein a means forrecognizing whether or not balls are held is provided.

2. Description of the Related Art

In the ball bump process which is applied in producing a semiconductordevice, bumps are formed of minute electroconductive balls on theelectrode portion (pad) of a semiconductor device or a PCB, and thesedevices and PCBs are bonded via the bumps with each other. In such aprocess, a ball-arranging substrate is used, in which minuteelectroconductive ball-arranging holes are formed, corresponding to thelocation of electrodes of the semiconductor device or a PCB.

In the process for forming bumps, the minute electroconductive balls aresucked and held in the ball-arranging through holes of theball-arranging substrate by means of vacuum suction, etc. It isnecessary that a single ball is exactly sucked in a single hole of theball-arranging substrate. If a ball is not sucked, then a bump is notformed on the electrode, and if two or more balls are sucked in a singleball-arranging hole, the bump may contact the adjacent pad.

As a method for recognizing such a ball-sucking failure, it is known toirradiate a laser beam from the lateral and the rear sides of theball-arranging substrate. If an error is recognized, the error isremoved by removing excess minute balls or repeating such aball-suction. When it is recognized that the balls are arranged on thesubstrate without an error, the ball-arranging substrate with the ballsas be are transported to a bump-bonding stage, where the locations ofthe minute electroconductive balls of the substrate and the electrodepads of a semiconductor device are aligned with each other.

After the completion of the alignment, the ball-arranging substrate, onwhich the minute electroconductive balls are sucked, is lowered down onthe semiconductor device, and then the minute electroconductive ballsand the electrode pads are bonded with each other by means of heatpressing. In the case when bumps are formed of a low melting point metalat the electrode portions of a PCB, it is general that a flux is appliedto the electrode portions, and minute balls are arranged at theelectrode portions and then reflowed.

As set forth above, the prior art inspection for excess balls or lack ofsucked balls includes a method for inspecting excess balls or lack ofballs by irradiating light from the front or lateral side of theball-arranging substrate. If there is lack of a ball, the lightirradiated from the front side of the substrate reaches, through theopen ball-arranging hole, the light-receiver located on the rear side ofthe ball-arranging substrate, so that lack of a ball can be detected. Ifthere are excess balls, the light irradiated from the lateral side ofthe substrate is shut out, and thus the light does not reach thelight-receiver located on the opposite side of the ball-arrangingsubstrate, so that excess balls can be detected. However, this method ofinspection does not have reproducibility in recognizing defects of theballs and is not used, in industrial production, when the diameter ofthe balls is less than 300 μm, particularly less than 200 μm, becausethe amount of light and the accuracy of the location recognition are notsufficient.

On the other hand, another method using the image-recognization methodis known for inspecting the arranged balls. According to the method, thelight is irradiated to the minute balls, which are held on theball-arranging substrate, and the reflected light is inspected by a CCDcamera. The reflected light is converted to binary images, i.e., thelight reflected by the balls is converted to white image, and the lightreflected by the substrate is converted to black image. Thus, theball-arranging condition is recognized.

However, it has been considered that it was difficult to exactlyrecognize the minute balls sucked and held-on the ball-arrangingsubstrate by the image recognizing method and this method was notapplied in the industry. For example, in the case when theball-arranging substrate is made up of a metal, e.g. stainless steel,the light reflected at the substrate itself causes erroneousrecognization e.g. due to reflections from machinery defect and damageportions or due to insufficient intensity difference between the lightreflected by the minute balls and that reflected by the ball-arrangingsubstrate itself causing an insufficient contrast. Also burrs may beformed on the substrate, when metal working, e.g., mechanical working,electrodischarging and laser irradiation is applied. In such a case, theaccuracy was remarkably influenced when the minute balls, whose diameterwas less than 200 μm, were mounted on the chip, etc.

Furthermore, when the substrate used is made of glass, the irradiatedlight is transmitted through the glass and reaches the jig, which holdsthe glass substrate, and the light reflected by the jig causes errors inrecognition of the balls as a metal arranging substrate does. That is,the transmitted light is irregularly reflected near the ball suckinghole to provide white bright images, causing the recognition of suckedballs to be uncertain. And the light is reflected by the defectsscattered on the surface of the substrate, where the reflected lightalso gives white images. Such a reflected light may be erroneouslyrecognized to be caused by the sucked minute balls.

The object of the present invention is to provide a ball arrangingsubstrate, arranging head, arranging apparatus and arranging method, inwhich the conditions of sucked balls more precisely than before, bywhich ball bumps can be formed more exactly.

For example, as disclosed in Japanese Unexamined Patent Publication No.4-250643, a conventional ball-arranging substrate is produced by formingball-arranging holes on the substrate of a metal, e.g., stainless steelor a ceramic material, etc. by means of precise electrodischarging,laser-irradiation, electroforming, etching, etc.

When the ball-arranging substrate is a metal, e.g., stainless steel,misalignment is caused by thermal expansion of the arranging substrateduring aligning between the ball-arranging holes and the electrodes dueto a large difference in the thermal expansion coefficient between ametal substrate and silicon chip. When the ball-arranging holes areformed by means of laser irradiation or electrodischarging, aprotuberance is formed around the holes and thus, dispersion of theheight of sucked balls and a decrease in the sucking capability areobserved. Furthermore, in the prior art it was difficult to preciselyopen the ball-arranging holes, of a diameter less than 100 μm, by meansof a general purpose working apparatus. If the diameter of theball-arranging holes must be less than 100 μm, the opened holes arenarrowed by means of metal plating. However, the number of workingprocesses is increased and the diameter of the opened holes is notformed uniformly, and the shapes of the holes are not formed as truecircles. Thus, these defects result in misplacement of the arrangedballs, and when bumps formed on a semiconductor device, or innerlead ofTAB, or a printed circuit board, etc. are arranged at a narrow pitch,the precision of the ball arrangement is lowered.

Japanese Unexamined Patent Publication No. 7-95554, discloses aball-arranging glass substrate. However, the disclosed substrate is notsuitable for arranging minute electroconductive balls.

Another object of the present invention is to provide a ball-arrangingsubstrate, a ball-arranging head, and an apparatus for arranging ballsand also a method for arranging balls, in which the minute balls arearranged more precisely than before, and thus ball-bumps. are formedmore exactly.

DISCLOSURE OF THE INVENTION

In order to achieve the object set forth above, the present inventionprovides the following:

(1) A ball-arranging substrate comprising:

a substrate having a main surface; and

a plurality of ball-arranging holes which are provided on said mainsurface at locations corresponding to those of the electrodes of asemiconductor device or a printed circuit board, etc., for sucking andholding minute electroconductive balls in said ball-arranging holes;

wherein when light illuminates the ball-arranging surface with saidsucked minute electroconductive balls, to optically recognize theconditions of arrangement of said minute electroconductive balls bymeans of the light reflected by said minute electroconductive balls andby said ball-arranging surface, the wavelength of said light emitted bya light source is selected in the range of 300 to 900 nm, and thereflectivity of said ball-arranging substrate for light from said lightsource is not more than 50%, provided that a reflective mirror may beprovided on the rear surface of said ball-arranging substrate oppositeto said light source, in the case when said ball-arranging substrate istransparent to the irradiated light.

(2) A ball-arranging substrate according to said (1), wherein aanti-reflection film is formed on said ball-arranging surface on whichsaid minute electroconductive balls to be sucked and held.

(3) A ball-arranging substrate according to (1) or (2), wherein saidball-arranging substrate is made of glass.

(4) A ball-arranging substrate according to (3), wherein said substrateis made of photosensitive glass.

(5) A ball-arranging substrate according to anyone of (1) to (4),wherein the ratio of the diameter of said ball-arranging holes on theside of minute electroconductive ball-arrangement to the diameter ofsaid minute electroconductive balls is in the range of from 1/3 to 4/5;and,

the thickness of said ball-arranging substrate is in the range of from0.3 to 1.0 mm.

(6) A ball-arranging substrate according to (1) to (5), wherein thediameter of said minute electroconductive ball is in the range of 20 to200 μm.

(7) A ball-arranging substrate according to (1) to (6), wherein saidreflectivity of said ball-arranging substrate is not more than 30%.

(8) A minute electroconductive ball-arranging glass substratecomprising: a plurality of ball-arranging holes, the diameters of whichare smaller than those of said minute electroconductive balls, forarranging said minute electroconductive balls at locations correspondingto those of the electrodes of a semiconductor device or a printedcircuit board,

wherein the ratio of the diameter of said ball-arranging holes to thatof said minute electroconductive balls is in the range of from 1/3 to4/5, the diameter of said ball-arranging holes being measured on thesurface of said minute electroconductive ball-arranging glass substrate;and the thickness of said minute electroconductive ball-arranging glasssubstrate is in the range of from 0.3 to 1.0 mm.

(9) A minute electroconductive ball-arranging glass substrate accordingto (8), wherein said ball-arranging glass substrate is made ofphotosensitives glass.

(10) A minute electroconductive ball-arranging head, comprising:

a minute electroconductive ball-arranging substrate in accordance with(1) to (9); and,

a means for holding minute electroconductive balls, provided with avacuum space for sucking said minute electroconductive balls, on theother surface of said substrate opposite to the surface holding theminute electroconductive balls.

(11) A minute electroconductive ball-arranging apparatus comprising:

a minute electroconductive ball-arranging head in accordance with (10);

light sources for illuminating the electroconductive balls holdingsurface of said ball arranging substrate;

a light-receiver for receiving light reflected by said ball arrangingsubstrate after being emitted from said light sources; and,

an image-recognizing and treating means for recognizing the conditionsof the arrangement of said minute electroconductive balls on saidball-arranging substrate, based on the output from said light-receiver,said image-recognizing and-treating means examining the conditions ofarrangement of said electroconductive balls after said electroconductiveballs are arranged on said ball-arranging substrate.

(12) A ball-arranging apparatus accordance with (11), wherein thearrangement of the electroconductive balls on said ball-arrangingsubstrate is repeated again if the conditions of the arrangement of theelectroconductive balls are found to be inappropriate as a result ofsaid examination.

(13) A method for arranging balls comprising the steps of:

sucking and holding to arrange minute electroconductive balls on asurface of a minute electroconductive ball-arranging substrate,corresponding to the locations of the electrodes of a semiconductordevice or a printed circuit board; and

illuminating said surface, on which said minute electroconductive ballswere sucked, and recognizing conditions of arrangement of said minuteelectroconductive balls using the light reflected by said minuteelectroconductive balls and that reflected by said minuteelectroconductive ball-arranging surface,

wherein the wave length of a light source is set in a range of 300 to900 nm, and the reflectivity of the light from said light source by theminute electroconductive ball-arranging surface, is made not more than50%.

(14) A method for arranging minute electroconductive balls according to(13), wherein said ball-arranging substrate is in accordance with (1) to(9).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a ball-type bump bonding apparatus,in which its entire construction is illustrated.

FIG. 2 is a schematic diagram for illustrating ball-arranging operationby means of a ball-arranging mechanism.

FIG. 3 is a schematic diagram for bonding balls to leads of afilm-carrier.

FIG. 4 is a schematic diagram for bonding balls to electrode pads of asemiconductor chip.

FIG. 5 is a cross-sectional view of an example of a ball-arranging head.

FIG. 6A is a perspective view of a minute electroconductiveball-arranging substrate for illustrating an example of holes arrangedin the form of a grid, and FIG. 6B is a sectional view for illustratingsaid ball-arranging substrate and a jig for fixing the substrate.

FIG. 7A is a sectional view of a minute electroconductive ball-arrangingjig for illustrating an example of ball-sucking holes arranged in theform of a grit, and FIG. 7B is a view taken along arrow P in FIG. 7A.

FIG. 8 is a sectional view for illustrating the light reflection of theball-arranging substrate according to the invention.

FIGS. 9A and 9B are a perspective view and a sectional view of thesubstrate, respectively, for illustrating an example of theball-arranging substrate.

FIG. 10A is a diagram for illustrating the distribution of lightreflected by a minute ball and a ball-arranging substrate.

FIG. 10B is a diagram for illustrating the distribution of lightreflected by minute balls and a ball-arranging substrate.

FIGS. 11A to 11F illustrate cross-sectional views of a ball-arrangingsubstrates having various type of ball-arranging holes.

FIGS. 12A to 12C are a series of sectional views, illustrating a processfor producing minute electroconductive ball bumps using a ball-arrangingglass substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

At first, examples of the methods and apparatus for bonding ball-typebumps by means of the ball-arranging substrate according to the presentinvention will be described, although such examples are not intended tolimit the invention (the methods and apparatus are detailed in JapaneseUnexamined Patent Publication (Kokai) No. 7-153765).

As shown in FIG. 1, such an apparatus comprises, as the mainconstitution, a ball-arranging mechanism 1, a substrate-transportingmechanism 2, a ball-recognizing means 3 and a bonding stage 4. Such anapparatus may be constructed by adding a mechanism for arranging andbonding minute metallic balls to an apparatus comprising a bondingmechanism, e.g., an innerlead bonder.

As shown in FIG. 2, a ball-stocking tray 11 is vibrated in theball-arranging mechanism 1. Namely, minute metallic balls B are placedin a metallic ball-stocking tray 11, which is then vibrated by avibrator 12, e.g., a parts-feeder in order to float the balls Beffectively.

Then, the balls B are sucked to a ball sucking head 13, which comprisesa ball-arranging substrate 15 provided with sucking through-holes 14,the diameters of which are smaller than that of the balls. It ispreferable that the sucking through-holes 14 are provided for aplurality of semiconductor chips. The ball-sucking head 13 is lowereddown near the ball-stocking tray 11 to suck balls B by vacuum suctioninto the ball-sucking through-holes 14 of the ball-arranging substrate15. The lowering distance (a distance from the bottom of the tray to thearranging substrate) and the vibrating width of the ball-sucking head 13can be controlled in the order of 0.1 mm.

Next, the ball-sucking head 13 is raised upwards, and the excess ballsB′, which are not the vacuum sucked balls B are mechanically removed andrecovered. The ball-sucking heat 13 is slightly vibrated by means of avibrator 16 so that only the excess balls B′ are removed and thenormally sucked balls are not removed.

As shown in FIG. 3, after the excess balls B′ are removed, theball-sucking head 13 is moved to a so-called recognizing location, wherethe ball-arranging substrate 15 is illuminated by light sources 18located surrounding the ball-recognizing means 3, and the lacking ofballs to be sucked and the existence of excess balls are recognized bymeans of a ball recognizing means, e.g., a CDD camera. If such failuresare recognized, all of the sucked balls are recovered by means of vacuumleak and mechanical removal, and then the ball-sucking operation isrepeated again.

Next, the ball-adsorbing head 13 is transported to the bonding stage 4by means of the substrate-transporting mechanism 2. At this time, ballsB should not fall down due to vibration during transportation, etc.

Then, as shown in FIG. 3, the transported ball-adsorbing head 13 isturned over and fixed on a bonding stage 4, which is used also as adevice holding stage and fixed by vacuum suction. The balls B, which areheld on the ball-arranging substrate 15 of the ball-sucking head 13settled on the bonding stage 4, are aligned with the innerlead 20 of afilm carrier. Such an alignment may be carried out by an alignmentmechanism of the main apparatus. After the alignment is settled, balls Bare bonded (transferred) to the innerlead 20 by means of thetransferring mechanism of the innerlead bonder itself.

Alternately, as shown in FIG. 4, when the balls B are bonded to theelectrode pads of a semiconductor chip, the semiconductor chip 30 ismounted on the bonding stage 4. Then, the ball-sucking head 13 islowered without being turned over, and the balls B are contacted withand bonded to the electrode pads of the semiconductor chip 30, while theball-sucking head 13 is heated by means of a heating tool 31.

In the above, the present invention is described referring to thepreferred embodiments for forming bumps by means of the ball-arrangingsubstrate. However, it is to be noted that the present invention shouldnot be limited solely to these embodiments.

Nextly, as an embodiment of the present invention, an example of aball-arranging head comprising a ball-arranging substrate of glass willbe described.

As shown in FIG. 5, a ball-arranging glass substrate 41 is fixed to aarranging substrate-holding jig of stainless steel 49 by evacuating itsvacuum space 48 for sucking an arranging substrate 41. For example, anumber of minute balls 43 of 60 μm in diameter which are composed ofmainly gold, are sucked and held by evacuating the ball-sucking vacuumspaces 47 which are provided in the jig 49 for fixing the ball-arrangingsubstrate 41.

The ball-arranging substrate 41 has ball-arranging holes 42 of e.g., 30μm, in diameter, i.e., a half of that of the balls. The balls 43 areheld in the ball-arranging holes 42 by evacuating the ball-suckingvacuum spaces 47 formed in the jig 49, from the rear surface of theball-arranging substrate 41.

Although the arranging substrate 41 is evacuated by evacuating thearranging substrate-sucking vacuum space 48 in this example, it ispossible to apply a unified type ball-sucking and transferring head, inwhich the ball-arranging substrate 41 is fixed on the jig 49, while thesubstrate-adsorbing vacuum spaces 48 are omitted.

In addition, the jig 49 for fixing an arranging substrate of the presentinvention may be provided with a heating mechanism, allowing bonding theballs by heating the balls.

If the ball-sucking vacuum space provided in the jig for fixing anarranging substrate is too large, and the contact area of an arrangingsubstrate with the substrate-fixing jig around the balls is too small,the ball-arranging substrate may not withstand the bonding pressure. Inorder to eliminate such a break, it is preferable to form theball-sucking vacuum spaces 47 as ditches or grooves having a width of 10to 100 times as large as the diameter of the ball-arranging holes 42.

However, where the balls are sucked and arranged in the ball-arrangingholes 42, which are arranged in the form of a grid, in theball-arranging substrate 41 as shown in FIGS. 6A and 6B, it is necessaryto provide extruding pillars 50 in order to increase the contact areabetween the substrate-fixing jig 49 and the ball-arranging substrate 41,as shown in FIGS. 7A and 7B. In order to provide such a contact area, asin other examples, it may be possible to apply a porous material to theball-sucking vacuum space 47 a or to a substrate-fixing jig 49 itself.

Turning to the process for bonding balls as shown in FIGS. 1 to 4, animage-recognizing method is used in the inspecting step after thesucking of minute electroconductive balls, which are sucked and held onthe ball-arranging surface of a ball-arranging substrate in thelocations corresponding to those of the electrodes of a semiconductordevice or a printed circuit board. Such an image-recognizing methodcomprises the steps of illuminating the ball-arranging substrate and theminute balls sucked and held thereon, and optically examining theirreflected light by means of a CCD camera.

The reflectivity of a ball-arranging substrate according to theinvention is meant by the ratio of the entire reflected light R to theincident light A, where the entire reflected light contains light breflected by the front surface s of the ball-arranging substrate S,light c reflected by the rear surface r of the ball-arranging substrateS and light d reflected by the substrate-fixing jig J located on therear surfacer of the ball-arranging substrate S, as shown in FIG. 8, inwhich B and T are designated for the minute balls and the transmittedlight, respectively.

When the light reflected solely by the substrate is measured, light dreflected by the jig J does not exist. Therefore, in such a case thereflected light is measured by placing a reflective mirror on the rearsurface of the substrate.

The present invention resides in improving the accuracy of recognizingthe conditions of arrangement of the sucked minute balls, wherebydecreasing the reflectivity of the ball-arranging substrate, as setforth above, down to not more than 50%.

According to a preferred embodiment of the present invention, as shownin FIGS. 9A and 9B, the ball-arranging substrate 51 is provided withball-arranging holes 52 each located in the locations corresponding tothose of the electrodes of a semiconductor device or a printed circuitboard, and thus minute electroconductive balls 53 are sucked and held onthe ball-arranging surface, wherein an anti-reflection film, preferablymade of a coating film 54 as described later, is formed on theball-arranging surface of the ball-arranging substrate 51.

When a xenon lamp is used as a recognizing light source, the amount oflight reflected by the ball-arranging substrate 51 is made to be notmore than 50%, preferably not more than 30%. It is possible to recognizethe image more exactly, while the contrast between the minuteelectroconductive balls 53 and the ball-arranging substrate 51 is mademore clearly, by reducing the amount of light reflected by theball-arranging substrate 51.

According to the image recognizing method, the image taken by a CCDcamera is generally depicted on a gray scale image picture 256 tonescorresponding to the amount of the incident light. A threshold value ispredetermined among the 256 tones, and the binary image (white or black)is judged using the threshold value. FIG. 10A illustrates an example ofthe distributions of the amount of light reflected by the minute ballsand the ball-arranging substrate. When the distributions of thereflected lights overlap as in this example, it is difficult todiscriminate the minute balls from the ball-arranging substrate by meansof the binary image method.

As shown in FIG. 10B, it is possible to exactly discriminate the minuteballs 53 from the ball-arranging substrate 51 by the binary imagemethod, owing to the difference in the amount of reflected lighttherebetween, by using the ball-arranging substrate 51 according to thepresent invention. The reflectivity of the coated ball-arrangingsubstrate 51, as shown in FIG. 10A, is about 25 to 30% in the entirerange of wave length of the incident light of 400 to 800 nm. Althoughthe degree of tone of light reflected by the minute balls may fluctuatedue to the deviation in the material and the surface condition of theminute balls 53, it is possible to discriminate the balls from thesubstrate irrespective of the conditions of the minute balls 53, whenthe ball-arranging substrate 51 according to the present invention isused. Particularly, when the reflectivity of the ball-arrangingsubstrate 51 is more than 50%, minute balls 53 may have such a value ofthe reflectivity depending on their surface conditions, and thus it maybe difficult to distinguish them from each other.

In order to decrease the reflectivity of the ball-arranging substrate,it is possible to use a black material 51 itself, or rather simply acommon substrate, the surface of which is coated with a nearly blackfilm 54 to reduce its cost. The term “nearly black” means riot to bestrictly black, but any color which is capable of depressing thereflection of light, e.g., dark brown or deep blue when a white light isused. The process for coating the substrate may be effected bysputtering, vacuum evaporation, ion plating, chemical vapor deposition,plating or painting. Any material capable of reducing reflection may beused as a coating film, for example, oxides (W₂O₃, Fe₂O₃, chromiumoxide, etc.), nitrides (SiN, TiN, etc.), carbides (SiC, TiC, etc.).

Also, oxides which exhibit a complicating crystal structure, such asperovskite, or even an amorphous structure may be used. The coating mayutilize multi-reflection by a multilayered structure, or may be formedby coating and drying a solution containing a nearly black powder. Atransparent film (e.g., SiO₂), may be laminated on the coating to form asandwiched structure having such a dark colored layer therebetween. Thethickness of the coating film has been checked in the range of 0.05 to100 μm. When a transparent glass is used as the ball-arranging substrate51, the jig for holding the ball-arranging substrate also reflectslight. Such a reflection can be prevented by coating the surface of theball-arranging substrate.

In the prior art, a metallic ball-arranging substrate may causedisplacement between the electrodes and the arranging holes due to alarge difference in thermal expansion coefficient between the substrateand a silicon chip, etc., when they are bonded at elevated temperature.Contrary to this, when the substrate is made of a glass, which has alower thermal expansion coefficient than a metal, it is possible toachieve ball-bonding with an improved accuracy even at a hightemperature and thus to effectively adapt to the recent requirement,i.e., decreasing in the size of balls and also the pitch between thearranged electrodes. The photosensitive glass is superior to the commonglass for forming minute ball-arranging holes in a more accurate manner,and thus it is possible to form fine ball-arranging holes with true holeshape and thus reduce the amount of light reflected by the edge of theholes, and to improve the accuracy of mounting the minute balls on achip, etc.

The light applied for recognizing the image may be incident in adirection either vertical or oblique to the minute balls. As a lightreceptor, one or more (either black and white or colored) CCD camerasand also a line sensor, etc. may be used.

It is possible to reduce the amount of reflected light from the surfaceof a ball-arranging substrate by forming minute roughness on the surfaceof a substrate by means of sandblasting, etc.

The ball-arranging substrate according to the present invention may beapplied not only to arrange gold or solder balls on a chip, but also toarrange gold or solder balls on the electrodes of a film-carrier of theso-called TAB, etc., or to arrange such balls on the electrodes of aprinted circuit board, etc. It is possible to form ball-bumps with avery high accuracy, when a ball-arranging substrate according to thepresent invention is combined with a head containing a holding meanswhich is provided with a vacuum space for holding the ball-arrangingsubstrate and the minute balls on the side opposite to the surface forholding the ball-arranging substrate. It is also advantageous forrecognizing the image to use a ball-arranging black substrate, also in amethod for holding minute balls other than suction.

As a preferable embodiment of the present invention, the ball-arrangingsubstrate is made of a glass. Particularly by using a glass whosethermal expansion coefficient is lower than that of a metal such asstainless steel and nearly equal to that of silicon, it is possible toreduce the misalignment between the minute electroconductive ball andthe electrode portion even when thermo-compression bonding is effectedat a high temperature.

When a minute ball may happen to thrust into an opening of theball-arranging substrate due to the high pressure bonding, it is easy toremove such a ball by immersing the glass substrate into an acid oralkaline solution which dissolves the metal. Contrary to this, when aball-arranging substrate is made of a metal, it is difficult tocompletely remove the minute ball thrust into an opening, because themetallic substrate itself may be dissolved into above solutions.

When the thermal expansion coefficient of a ball-arranging substratemade of a glass is in a range of (1 to 100)×10⁻⁷/° C., preferably in therange of (20 to 90)×10⁻⁷/° C., i.e., from about 40×10⁻⁷/° C. of thecoefficient of silicon to the twice thereof, it is possible toconsiderably reduce the occurrence of misalignment in comparison withthe case of a ball-arranging metallic substrate. Furthermore, aphotosensitive glass is capable of forming minute holes superior intheir shape and in precise locations, and thus it is possible to formball bumps with a fine pitch (not more than 300 μm, particularly notmore than 100 μm) without occurrence of displacement.

In addition, it is possible to at once open all the holes by exposing aphotosensitive glass through a mask, and thus to produce aball-arranging substrate at a very low cost. Such an advantage isparticularly evident in the production of a ball-arranging substratehaving not less than 100 holes (particularly, not less than 300 holes)all at once. Contrary to this, when the holes are opened one by one,e.g., by means of electric discharge working, if forming a ball at onlyone hole is failed, it is necessary to repeat the whole openingoperations, and thus the yield of the substrate is reduced. In addition,it is possible to easily form alignment marks in optional numbers atoptional locations, which marks can be used to aligning the electrodeportion for forming bumps.

A photosensitive glass, which is capable of being applied to theproduction of a ball-arranging substrate according to the presentinvention, may be SiO₂—Al₂O₃—LiO based glass containing Ag, Au, Cu, etc.as a photosensitive metal. If necessary, it is possible to add CeO₂,etc. as a photosensitizating agent. After the both surfaces of thephotosensitive glass plate are polished, a mask, in which a pattern ofholes is provided in appropriate location corresponding to those of theelectrodes of a semiconductor device, etc., is placed on a surface of apolished glass plate. Then, the surface is irradiated by ultravioletrays to expose opening portions of glass. After the mask is removed, anappropriate thermal treatment is effected to crystallize the irradiatedportions of the glass, which are then dissolved by means of an acid toform the desired ball-arranging holes.

It is possible to form bumps with an accuracy of not more than ±5 μm,preferably not more than ±3 μm, from the centers of the balls and thecenters of corresponding Al electrode pads, etc. on a semiconductordevice, by using the ball-arranging substrate according to the presentinvention which has the holes with an accuracy of the location of notmore than ±5 μm, preferably not more than ±3 μm.

In the process set forth above, the holes are opened in a glasssubstrate where the exposed portions are liable to be etched by an acid,it is also possible to open the similar holes by selecting aphotosensitive glass, in which the portions irradiated by ultravioletrays are difficult to etch with an acid.

This ball-arranging substrate may be used in combination with a head,which can apply a pressure or heat at the time of arranging the balls.In such a case, a certain thickness of the ball-arranging substrate isnecessary to exhibit a strength, which is bearable to the pressureeffected in the bonding operation. However, in the case of thick glassit is difficult to etch glass by acid, etc. The present inventors foundthat a thickness of 0.1 to 1.0 mm is appropriate to open uniform holes,after investigating ball-arranging substrates having variousthicknesses.

Although the thickness of a glass substrate is limited as set forthabove, 10% of the ball-arranging glass substrates suffered from crackingat an applied 5 kg force for bonding when the thickness is less than0.25 mm. Contrary to this, substrates of 0.3 mm in thickness did notsuffer from cracking even after 10,000 operations, bonding, and thusthey can be successfully used in production. On the other hand, a glasssubstrate, whose thickness is not less than 1 mm, exhibitsdisadvantages, i.e., when the glass substrate is etched to open theholes, the etching time increased and it was difficult to uniformly formthe diameter of the opened holes over a prolonged etching time.Therefore, it was clear that the thickness of a ball-arranging glasssubstrate should preferably be not thinner than 0.3 mm and not thickerthan 1.0 mm, according to the present invention.

In order to apply minute balls to the ball-arranging substrate, it wasnecessary to optimize not only its thickness but also the diameter ofthe holes for sucking and holding the balls, by various experiments.That the diameter of the arranging holes is simply smaller than that ofthe minute electroconductive balls is not sufficient to successivelyexecute the ball-arranging operation by means of suction or evacuation.If the ratio of the diameter of the holes to that of the balls is lessthan 1/3, the efficiency of suction decreases. According to theinventor's experiments, for example, the percent ratio of success inholding by sucking 500 minute solder balls of 80 μm in diameter was 80to 87%, when the diameter of the holes in the ball-arranging substratewas not more than 20 μm. Contrarily to them, the percent ratio ofsuccess was not less than 95%, when the diameter of the holes was set tonot less than 25 μm.

In addition, it was clarified after the inventor's detailed experimentsthat the minute balls thrust into the holes by the pressure effected bytransferring the minute balls on the electrodes, when the ratio of thediameter of the ball-arranging holes to that of the minuteelectroconductive balls exceeds 4/5. For example, when 300 gold balls 40μm in diameter were held on a ball-arranging substrate having holes 34μm in diameter and the balls were pressed on the substrate with apressure of 20 g/ball, 52 balls among 300 balls were thrust into theholes of the ball-arranging substrate, and thus the ball-bonding was notcompleted. Contrary to this, when the diameter of the holes was set to32 μm and the other condition was the same as in the experiment setforth above, no ball thrust occurred. Therefore, it was first clarifiedaccording to the present invention that the ratio of the diameter of theball-arranging holes to that of the minute electroconductive ballsshould be in the range of from 1/3 to 4/5. In the case of a metallicsubstrate, e.g. of stainless steel, such a relationship between thediameters of the holes of the substrate and the minute balls was notclearly observed because the edge of the holes was swollen when theholes were formed by electric discharge working.

It is appropriate that the preferable ball-arranging glass substrate isused by coating an anti-reflection film and thus decreasing thereflectivity down to not more than 50% as set forth above. However, itshould be noted that the limitations of the diameter of the holes andthe thickness of the ball-arranging substrate themselves arecharacteristic factors of the present invention and constitute anindependent invention.

Several examples of the form of holes opened in the substrate are shownin FIGS. 11A to 11F. In the drawings, the surface for use in arrangingthe balls is defined as the front surface. FIG. 11A illustrates asubstrate where the diameter of a hole is the same on the front and rearsurfaces. In FIG. 11B, the diameter of a hole is smaller on the frontsurface than on the rear surface. In FIG. 11C, the size of the diameterof a hole is larger on the front surface than the rear surface reverselyto FIG. 11B. FIG. 11D illustrates a substrate as shown in FIG. 11A,which was machined to have larger diameter on the front surface and theedge around the hole near to the front surface was cut off. In FIG. 11E,the substrate shown in FIG. 11D was further machined to have the edgenear to the rear surface was cut off. FIG. 11F illustrates a substratehaving a mixed type of FIG. 11B and FIG. 11C, in which the diameter of ahole is larger near to the both surfaces and grows smaller toward insidethe substrate.

The ball-arranging substrate shown in FIG. 11B is advantageous inpreparing the suction system, because the diameter of the holes islarger on the reduced pressure side than in the ball-sucking surface (itis necessary to prepare a groove pattern for providing vacuum in aball-arranging head in the locations for holding the substratecorresponding to the locations of the holes of the arranging-substrate.If the diameter and the pitch of the holes are narrow, it is difficultto prepare such a groove pattern).

In the preparation of the substrates as shown in FIGS. 11D, 11E and 11F,the ball-arranging holes can be worked by means of either acid etchingor mechanical polishing. And the edge of the holes may be eitherlinearly tapered or smoothly curved. In FIGS. 11E and 11F, the diametersof the holes may be equal to or different from each other on the frontand rear surface sides, however it is desirable that the minimumdiameter of the hole, where the minute balls on the front surface aresucked and held, is in the range of 1/3 to 4/5 of the diameter of theminute ball.

The ball-arranging substrate according to the present invention may beapplied to arrange gold or solder balls on the electrodes of a filmcarrier, e.g., TAB, etc., and to arrange such balls on the electrode ofa printed circuit board, other than the arrangement of such balls on achip as detailed in the Example set forth below. It is possible toprepare extraordinarily precise ball bumps, by using a head in which aball-arranging substrate made of glass according to the presentinvention is combined with a means for holding the ball-arrangingsubstrate and the minute electroconductive balls provided with a vacuumspace on the side opposite to the side of holding the balls.

EXAMPLES

An example, to examine errors in sucking minute balls by means of aball-arranging substrate according to the present invention, will bedescribed.

Ball-arranging glass substrates, each coated with a coating film ofW₂O₅, Fe₂O₃, TiN or TiC, were prepared. A so-called image-recognizationtest by means of a CCD camera was effected on these substrates, on thesurface of which minute electroconductive balls were sucked. Table 1also shows the results using a bare glass substrate.

TABLE 1 Coating film Result No film (comparative) x W₂O₅ ∘ Fe₂O₃ ∘ TiN ∘TiC ∘ Chromium oxide ∘ Perovskite structure ∘ oxide (Y—Ba—Cu—O)

The errors in the minute electroconductive ball-adsorption were examinedby the image-recognization test under the following conditions:

Ball-arranging substrate=photosensitive glass

Number of the sucking holes of the substrate: 300

The diameter of the sucking balls (μm): 30, 60, 100, 150, 200, 300 and500

The material of the sucked balls:

Gold and solder

Light source: Xenon lamp

Substrate with no coating (Comparative): reflectivity of 10 to 15%,transmissivity of 85 to 90%

Substrate with a coating:

reflectivity of 5 to 40%, transmissivity of 3 to 20%

Number of Experiments: 100

In the Table, the mark × shows the case in that sucking more or lessminute balls was judged as proper or appropriate sucking was judged asfailure, and the marks o show that recognition of existence of excessballs and holes lacking sucked balls could be exactly done. It is clearfrom the results that when the image recognition is made using a glasssubstrate with no coating, even excess or lacking of minute balls arejudged as correct and that the number of sucked minute balls was exactlyjudged in the cases of the coated glass substrates, in which the fivecoating films depressed the light reflection from the surface of theball-arranging substrate. The erroneous recognition occurred at a rateof 15% in average for the bare substrate.

It is possible to exactly produce bumps on the minute ball-arrangingsubstrate according to the present invention, even if the diameter ofthe balls and the pitch of arranging balls are modified due to thefuture trend of semiconductor devices.

Thus, according to the present invention, it is possible to formprecisely minute electroconductive bumps on the electrodes of asemiconductor chip, a film-carrier or a printed circuit board, becausethe light reflected by the surface of a ball-arranging substrate isdepressed and thus the accuracy of image recognization isextraordinarily improved in the inspection of the minute balls sucked onthe ball-arranging substrate.

A ball-arranging head as shown in FIG. 5 was used to produce minuteelectroconductive ball bumps.

Referring to FIG. 12A, a ball-arranging substrate 41 is moved over asemiconductor chip 45 and the locations of the balls 43 and theelectrode pads 44 are aligned. A rapid alignment can be done by usingthe alignment marks formed on the ball-arranging substrate 41.

As shown in FIG. 12B, the balls 43 held by the substrate are lowered andpressed down onto the pads 44 of the semiconductor chip 45 mounted onthe support 46 with a pressure of 10 to 30 gf per one ball.

As shown in FIG. 12C, all the balls 43 are bonded to the pads 44, andthen the reduced pressure space 47 for sucking the balls is pressurizedto atmospheric pressure, and the ball-arranging substrate 1 is movedupwards.

In this example in which the minute electroconductive balls 43 aresucked and held on the substrate 41, no lack of balls occurs or noexcess balls are sucked due to the lack of suction or the leak of airgenerated by an inappropriate shape of the holes. The semiconductor chip45 provided on its support 46 is heated up to 300 to 500° C. The bumpsare bonded to the electrodes while forming an Al—Au-based alloy, withoutfailure. The displacement of the bonded gold balls due to the influenceof the heat at the time of forming bumps was not more than ±3 μm. Thedeviation of the height of bumps was not more than ±2 μm. Furthermore,when a thus bump-provided semiconductor chip was transported, no bumpsfell off. In addition, when such a bump-provided semiconductor chip 45was bonded to an innerlead of a film-carrier, it was confirmed that theleads did not flow and fall off.

On the other hand, when ball-bumps were formed by means of aball-arranging stainless steel substrate, in which ball-arranging holeswere formed by means of electrical discharge working, the displacementof the formed bumps was more than ±10 μm, while the other conditionswere the same as those set forth above, and the deviation of the heightof the formed bumps was in the range of ±7 μm.

As illustrated in the above experiment, in a minute electroconductiveball-arranging substrate or a minute electroconductive ball-arranginghead, by using a glass substrate, and by improving the precision of thelocation and the shape of the ball-arranging holes, it was possible toextraordinarily improve the accuracy in setting the ball-arranginglocation, which allows forming minute electroconductive bumps with ahigh accuracy on the electrodes of a semiconductor chip, a film-carrieror a printed circuit board.

What is claimed is:
 1. A ball-arranging substrate comprising: asubstrate having a main surface; and a plurality of ball-arranging holeswhich are provided on said main surface at locations corresponding tothose of electrodes of a semiconductor device or a printed circuitboard, etc., to suck and hold minute electroconductive balls in saidball-arranging holes; wherein when light illuminates said ball-arrangingsurface, the conditions of arrangement of said minute electroconductiveballs are optically recognized by means of the light reflected by saidminute electroconductive balls and by said ball-arranged surface, thewave length of the light of a light source is set in the range of 300 to900 nm, and the reflectivity of light from the light source is made notmore than 50%, provided that a reflective mirror is arranged on the rearsurface of said ball-arranging substrate opposite to said light source,in the case when said ball-arranging substrate is transparent to theirradiated light.
 2. A ball-arranging substrate according to claim 1,wherein a reflection-reducing film is formed on said ball-arrangingsurface on which said minute electroconductive balls are sucked andheld.
 3. A ball-arranging substrate according to claim 1, wherein saidball-arranging substrate is made of glass.
 4. A ball-arranging substrateaccording to claim 3, wherein said substrate is made of a photosensitiveglass.
 5. A ball-arranging substrate according to claim 1, wherein theratio of the diameter of said ball-arranging holes on saidball-arranging surface to the diameter of said minute electroconductiveballs is in the range of from 1/3 to 4/5, and the thickness of saidball-arranging substrate is in the range of from 0.3 to 1.0 mm.
 6. Aball-arranging substrate according claim 1, wherein the diameter of saidminute electroconductive ball is in the range of 20 to 300 μm.
 7. Aball-arranging substrate according to claim 1, wherein said reflectivityof said ball-arranging substrate is not more than 30%.
 8. A minuteelectroconductive ball-arranging head, comprising: a minuteelectroconductive ball-arranging substrate claimed in claim 1; and, ameans for holding said minute electroconductive balls, provided with avacuum space for sucking said minute electroconductive balls on thesurface of said substrate opposite to the surface, for holding saidminute electroconductive balls.
 9. A minute electroconductiveball-arranging apparatus, comprising: a minute electroconductiveball-arranging head claimed in claim 8; a light source for illuminatinga surface of said substrate on which said minute electroconductive ballsare held; a light-receiver for receiving light from said light sourceafter it is reflected by said substrate; and, an image-recognizing andtreating means for recognizing the conditions of the arrangement of saidminute electroconductive balls, which are arranged on said substrate,based on the output from said light-receiver, said image-recognizing andtreating means examining the conditions of the arrangement of theelectroconductive balls after said electroconductive balls are arrangedon said ball arranging substrate.
 10. An apparatus for arranging minuteelectroconductive balls according to claim 9, wherein arranging of saidminute electroconductive balls is repeated on said minuteelectroconductive ball-arranging substrate is repeated, in the case whenthe conditions of arrangement of said minute electroconductive balls arenot appropriate.
 11. A method for arranging minute electroconductiveballs according to claim 8, wherein said ball-arranging substrate is onein accordance with any one of claims 1 to
 9. 12. A minuteelectroconductive ball-arranging substrate made of glass comprising aplurality of ball-arranging holes, the diameter of which is smaller thanthat of said minute electroconductive balls, to arrange said minuteelectroconductive balls at locations corresponding to those ofelectrodes of a semiconductor device or a printed circuit board, whereinthe ratio of the diameter of said ball-arranging holes to that of saidminute electroconductive balls is in the range of from 1/3 to 4/5, thediameter of said ball-arranging holes being measured on the side ofarranging said minute electroconductive balls of said ball-arrangingsubstrate; and the thickness of said minute electroconductiveball-arranging substrate is in the range of from 0.3 to 1.0 mm.
 13. Aminute electroconductive ball-arranging glass substrate according toclaim 12, wherein said substrate is made of a photosensitives glass. 14.A minute electroconductive ball-arranging head, comprising: a minuteelectroconductive ball-arranging substrate claimed in claim 12; and, ameans for holding said minute electroconductive balls, provided with avacuum space for sucking said minute electroconductive balls on thesurface of said substrate opposite to the surface, for holding saidminute electroconductive balls.
 15. A minute electroconductiveball-arranging apparatus, comprising: a minute electroconductiveball-arranging head claimed in claim 14; a light source for illuminatinga surface of said substrate on which said minute electroconductive ballsare held; a light-receiver for receiving light from said light sourceafter it is reflected by said substrate; and, an image-recognizing andtreating means for recognizing the conditions of the arrangement of saidminute electroconductive balls, which are arranged on said substrate,based on the output from said light-receiver, said image-recognizing andtreating means examining the conditions of the arrangement of theelectroconductive balls after said electroconductive balls are arrangedon said ball arranging substrate.
 16. An apparatus for arranging minuteelectroconductive balls according to claim 15, wherein arranging of saidminute electroconductive balls is repeated on said minuteelectroconductive ball-arranging substrate is repeated, in the case whenthe conditions of arrangement of said minute electroconductive balls arenot appropriate.
 17. A method for arranging minute electroconductiveballs, comprising the steps of: sucking and holding to arrange minuteelectroconductive balls on a surface of a minute electroconductiveball-arranging substrate, at locations corresponding to the locations ofelectrodes of a semiconductor device or a printed circuit board; andilluminating said surface holding said minute electroconductive balls torecognize the conditions of arrangement of said minute electroconductiveballs by using the light reflected by said minute electroconductiveballs and that reflected by said minute electroconductive ball-arrangingsurface, wherein the wave length of said illuminating light is set inthe range of 300 to 900 nm, and the reflectivity of the light reflectedby said minute electroconductive ball-arranging surface, is set to benot more than 50% based on the light source.